1. Field
The present invention relates to a technology for an electrode material capable of replacing a conventional Mo-based metal electrode material and a conventional ceramic-based electrode material, and more particularly to a technology for synthesizing composite materials by using the Mo and ceramic material and for using them as an electrode.
2. Description of Related Art
Alkali Metal Thermal to Electric Converter (AMTEC) is a thermal to electric power generator capable of generating electrical energy from thermal energy.
When a temperature difference is given to both ends of an ionically conductive Beta-Alumina Solid Electrolyte (BASE), Na charged in the cell is ionized into Na+ due to the vapor pressure difference of Na, and then is neutralized. Electricity is generated during this process.
In this case, low voltage and high current are generated. So, when the cells are modularized by being connected in series or in parallel, a large amount of electric power can be generated.
The development of alkali metal thermal to electric converter (AMTEC) technology has started for the purpose of an electric power source for space.
The AMTEC has a high power density per unit area and high efficiency, and maintains stability. The AMTEC uses a variety of heat sources, for example, solar energy, fossil fuel, waste heat, terrestrial heat, nuclear reactor, etc. The AMTEC is comprised of electric power generation cells capable of generating electricity without using a driver such as a turbine, a motor or the like, so that it can directly generate electricity from a portion contacting with the heat. When the AMTEC is formed in the form of a module in series or in parallel, a great amount of electricity of several KW to several hundredths MW can be generated.
At present, through a technology of collecting the waste heat, the waste heat is collected in the form of heat water, combustion air, etc., by using a heat exchanger, a waste heat boiler or the like.
The AMTEC is capable of improving the efficiency by directly generating high-quality electricity. Therefore, the AMTEC is now issued as a promising technology replacing the existing technologies.
One of the characteristics of the AMTEC power generation technology is to have a simpler structure and higher energy conversion efficiency than those of other thermal to electric converting elements.
Particularly, compared with a solar thermal power plant, the AMTEC power generation technology does not require a mechanical driver such as a turbine, etc. Compared with a thermoelectric device, the AMTEC power generation technology can be applied to a high capacity, a high efficiency system.
The process of generating electricity in the AMTEC will be specifically described. After the state of Na vapor is changed into a vapor state in a high temperature and high pressure evaporator by a heat source, Na+ passes through beta-alumina solid electrolyte (BASE), and free electrons return to a cathode through an electric load from an anode, and then are recombined with ion generated from the surface of a low temperature and low pressure BETA and then is neutralized. Electricity is generated during this process.
The vapor pressure of Na plays the most significant role in a thermal to electric power generator as an energy source or a driving force which generates electricity. Also, free electrons generated during a process in which Na passes through the solid electrolyte due to a concentration difference and temperature difference of a working fluid are collected through electrodes, so that electricity can be generated.
The beta-alumina and Na super-ionic conductor (NASICON) may be used as the solid electrolyte.
However, when NASICON is exposed at a high temperature for a long time, there is a problem in the stability thereof.
The beta-alumina includes two kinds of beta′-alumina and beta″-alumina.
The beta′-alumina has a more improved layer structure so that the conductivity of the Na+ ion is much better. Therefore, the beta″-alumina is now generally used.
A process is repeated in which the neutral Na vapor is condensed by being cooled on the inner surface of a low pressure condenser and is transferred to an evaporator by a capillary wick, and then is changed into a vapor state again. Generally, the temperature of the evaporator is in a range of 900 K to 1,100 K, and the temperature of the condenser in a range of 500 K to 600 K.
It is possible for the efficiency of the thermal to electric power generation of the AMTEC to be up to 40%. The AMTEC power generation technology has a high power density and a simple structure requiring no separate driver.
It is Mo-based metal electrode material and a ceramic-based electrode material like TiN, TiC, NbC, RuW, Ru2O, etc., that have been researched up to now and used in the AMTEC.
In Korean Patent No. 10-1101704, disclosed is an electrode for a thermoelectric device and a method for manufacturing the same. More specifically, the method includes: weighing Ni powder and Mo powder in such a manner as to form a composition of Ni1-XMoX (Here, 0.5≦X<1 and X is a real number), mixing the weighed Ni powder and the weighed Mo powder in such a manner as to form the composition of Ni1-XMoX (Here, 0.5≦X<1 and X is a real number), filling the mixed powder of the Ni powder and the Mo powder in a mold and setting in a chamber of a spark plasma sintering system, reducing the pressure of the inside of the chamber through the vacuumization and performing spark plasma sintering on the mixed powder by applying a DC pulse while pressurizing the mixed powder, obtaining a Ni1-XMoX sintered body (Here, 0.5≦X<1 and X is a real number) by cooling the temperature of the chamber. According to the present invention, since the temperature can be rapidly increased, it is possible to restrain grains from growing, to obtain a dense sintered body for a short time, to obtain a high dense electrode for a thermoelectric device, which can be sintered for a short time and has few pores and grains having a very dense gap therebetween. Since the electrode for a thermoelectric device has a much less thermal expansion coefficient difference from a thermoelectric semiconductor, CoSb3 than those of other electrode materials, it has less mismatch, for example, excitation at the interface with the thermoelectric semiconductor even at a high temperature, so that the reliability of the electrode for a thermoelectric device is high at a high temperature. However, there is still a requirement for an electrode having an excellent performance and an excellent durability by maintaining high electrical conductivity and by restraining the growth of the grain at a high temperature.